Not applicable.
FIELD OF THE INVENTION
This invention relates to a microphone assembly consisting of three or more microphone elements that are arranged to achieve a surround image for recording audio, especially audio synchronized with video. The outputs of the invention are compatible with current surround decoders.
Prior art multiplexing systems for reducing more than two audio channels to two audio channels are replete in the art. Common practice in this area involves encoding a two channel or stereo recording by means of multiplexing in order to establish more than two channels of sound in the two channel recording, which extra channels of sound typically are retrieved by a complementary reversal of the encoding process. The most notable is the system licensed under the trademark DOLBY PROLOGIC. Usually, a recording is encoded with a DOLBY SURROUND SOUND brand system for subsequent playback on a system equipped with a complementary proprietary decoding circuit which extracts so-called xe2x80x9cmatrixedxe2x80x9d information from the recording for playback through left, right, center, and rear speakers. This is a relatively simple process compared to the more complex quadraphonic matrixing systems of past. This proprietary system has grown in popularity due to prominence of encoded source material such as movies having surround sound soundtracks. More importantly, however, the DOLBY PROLOGIC brand decoder, along with the predecessor, the DOLBY SURROUND brand decoder, is compatible with playback of conventional stereo recordings and other sources and can provide pleasant results, especially with recordings having notable ambient content (e.g. recordings produced with a pair of microphones, one corresponding to one of the two stereo channels in the recording). This proprietary decoding process produces four channels of sound from the two channel input of a stereo recording or other source: Left, Right, Center, and Surround. The DOLBY standard includes additional parameters and specifications for the encode/decode process, such as bandwidth filters and delay, but it can be seen that decoding essentially consists of summing the Left and Right channels of stereo recording to produce the third xe2x80x9cCenterxe2x80x9d channel, and subtracting the Left channel information from the Right channel information to derive the fourth xe2x80x9cSurroundxe2x80x9d channel. The Surround channel thus essentially consists of information which is inherently out of phase between the Left and Right channels (i.e. generally a difference of 180 degrees). This encoding process makes use of the natural ability of the ear to perceive out-of-phase audio information to artificially create the Surround channel and store it as ambient or out-of-phase information on the Left and Right channels. Naturally, any out-of-phase or ambient information contained on a conventional stereo recording, such as a stereo recording of an orchestra, is also extracted by such a prior art decoder during playback and accordingly reproduced as xe2x80x9csurroundxe2x80x9d channel information, but not to any discernable degree, due to lack of strength of the out-of-phase signal. Similarly, xe2x80x9ccenterxe2x80x9d channel information contained on a conventional stereo recording or other source may be exaggerated when decoded during playback with this system""s decoder due to excessive center stage content contained in the conventional stereo recording.
Many microphone assemblies are known for monophonic and stereophonic recording, which assemblies can include a single or pair of microphone elements. Such prior art microphone assemblies are limited in their ability to reproduce a full, two dimensional sound field and in their ability to localize sound. While other microphone assemblies with more than two microphone elements can reproduce relatively full, two dimensional sound fields and can localize sounds, their outputs are not compatible with standard surround decoders. Also, they are deficient in their ability to reproduce what may be called a staging effect or surround image, which would be compatible with DOLBY SURROUND technology.
There is a need, therefore, for a microphone apparatus which can cheaply and reliably produce a surround image (as defined below), localize sounds and remain compatible with standard surround decoders.
Prior developments in this field may be generally illustrated by reference to the following U.S. Patent documents:
The disclosures of the above patent documents are incorporated herein by reference.
U.S. Pat. No. 3,872,249 shows a circuit for decoding an encoded or matrixed signal on a stereo channel (i.e. Left and Right channels) based on a known variable mixing ratio for matrixing at least four sound channels (i.e., Left Front, Right Front, Left Rear, and Right Rear). Passing similarity with the present invention lies in the general teaching of matrixing more than two channels into a two channel medium. In the case of the instant invention, however, no forced phase shifting (i.e. by use of electronics) occurs, as it does in this reference. Also, a multi-channel recording device, along with a multi-channel mixer, generally are required to produce an acceptable multi-channel recording in this reference.
U.S. Pat. No. 4,206,324 discloses a multi-element microphone assembly in which two microphone side element supports are pivotally disposed relative to a center fixed element support. The side supports are pivotally adjustable relative to the center fixed element, and the output levels of the side elements are electrically adjustable relative to the center element output. This reference does not show a rear microphone element, nor a matrixing circuit for four microphone elements.
U.S. Pat. No. 4,262,170 teaches a microphone system and circuitry for encoding multi-channel sound information picked up by its microphones into two channels (i.e. Left and Right) for subsequent playback by an SQ type quadraphonic sound system. Similarity with the present invention lies in the general teaching of a microphone apparatus and circuitry for encoding multiple channels into two channels, but the reference teaches subsequent playback on a system with complementary decoding. The actual circuit itself in one embodiment relies on signal phase shifting and amplification to encode the multiple channels, whereas the present circuit relies on signal amplification only. Other embodiments of this reference show various frequency-dependent phase-shifting and amplitude-adjusting circuits. The system of the present invention inherently incorporates natural phase shift in that information received by the rear microphone hereof generally is out-of-phase with the center microphone, in relation to the recording site. This reference further notes that Neuman Company of West Berlin, Germany, manufactures a 4-element adjustable microphone assembly.
U.S. Pat. No. 4,947,437 to Firebaugh teaches the use of a four-quadrant photoelectric microphone to produce unencoded stereo signals, which signals (apart from their creation by photoelectrically measuring acoustical displacement of a suspended ball at a single point in space) are entirely conventional stereo. That is to say, only combined center/left and combined center/right audio information is passed on to the left and right output signals, the rear audio information being subtracted out. The Firebaugh device does not encode and preserve surround information, as defined infra. A missing feature in Firebaugh (and other art) is the orientation of the microphone elements as related to 4-2-4 matrix inputs, which is required to acoustically capture the sound local to a camera in a way that when encoded with the 4-2-4 matrix produces a signal compatible with DOLBY SURROUND brand decoder technology. In addition, Firebaugh teaches elements that are equally sensitive throughout their entire area, lacking axial directions of maximum sensitivity.
Conventional stereo has an attribute known as stereo image, which is defined as the separation of a sound field into two regions, left and right. Dolby stereo has an attribute known as surround image, which is defined as the separation of a sound field into four regions, left, right, center, and rear. The surround image of this invention is created by the orientation of the four microphone elements in combination with the relative weighting of the four microphone signals, to achieve the surround image in a Dolby stereo signal.
A xe2x80x9csurround imagexe2x80x9d is defined for the purposes of the present invention as the orientation of four microphone elements so as to section the acoustic environment to be recorded into four regions that capture the main features of a stage environment (the environment of, for example, a live play produced on the stage of a commercial theater). These regions are labeled stage left (or left), stage right (or right), center stage (or center), and ambient (or rear). As has been shown in the theater industry and the commercial movie industry, this sectioning of the acoustic environment creates the most realistic sound from the point of view of the listener. Very likely, this is due to the familiarity of listeners with live entertainment, conventionally viewed and heard in real-life stage environments.
The microphone system of this invention differs from all other microphone systems by employing, and faithfully receiving for realistic reproduction, a surround image. FIG. 7 shows the orientation of the four microphone elements of this invention and how they appear in the acoustic environment in order to create this surround image.
Current electronic technology dictates that audio signals be transmitted and stored in a stereo format. For this reason, the four microphone element signals are encoded into stereo using the circuitry means shown in FIGS. 5 and 6.
Current commercial electronics technology also utilizes a standard method of two to four channel decoding, known under the trademark DOLBY SURROUND SOUND. The microphone apparatus described is completely compatible with this decoding method.
When this invention is compared to the prior art, for example, U.S. Pat. No. 4,262,170 to Bauer, it can be seen that the latter is comprised of a microphone with a separate chassis that houses extensive encoding circuitry. The present invention is comprised of a microphone assembly only, with a simple encoding scheme built in. The Bauer device works only with a complementary decoder by the same inventor, while the present invention works with standard industry decoders, without modification. One example of such a standard industry decoder is the Kenwood Audio/Video Surround Receiver, Model #107VR, available from Kenwood USA of Long Beach, Calif. The Bauer device attempts a three dimensional representation of the ambient acoustical environment, while the present invention creates a surround image similar to that used in cinema and the like (i.e., stereo with a monaural center channel and a monaural surround channel). While, as noted above, surround imaging is a somewhat artificial convention, the surround image effect is familiar to audiences, and therefore may be even more acceptable to them psychologically and physiologically than three dimensional sound.
Alternatively, the present invention may be understood as eliminating the need for DOLBY brand encoding or mixing during the production of a conventional two channel recording by providing an improved microphone assembly capable of capturing additional natural ambient information and distinguishing natural center and rear information that is present during recording. The stereo audio information from the microphone then requires only two channels of a recording device for recording.
An alternative implementation of this invention uses just three microphone elements. With the center channel microphone element eliminated, a virtual center channel is present at output Left and Right. This is due to the fact that the acoustical energy from stage center reaches the left and right microphone elements at the same time, thus creating a mono, i.e. center, signal at outputs LT and RT.
A further additional implementation uses a fifth microphone element as a second rear channel, analog to digital conversion, DSP processing and AES output to achieve compatibility with Dolby Digital 5.1 format.
It is the primary object of the invention to provide a microphone assembly utilizing a microphone array and an encoding circuit for producing a stereo composite signal equivalent to that required by movie and video industry surround decoders.
It is a further object of the invention to provide an improved microphone assembly which is free from the limitations of the prior art and which provides a surround image and localization of recorded sound.
It is a further object to of the invention to provide a microphone assembly including four microphones in which output signals from the microphones are combined into a surround stereo left and right composite signal.
It is a further object of the invention to provide a microphone assembly including four microphone elements which can take the form of a stand-alone microphone assembly.
It is a further object of the invention to provide a microphone assembly which is designed to attach externally to a video recording camera.
It is a further object of the invention to provide a microphone assembly which is integrated within a video recording camera body.
Another feature is an apparatus that is easy to use, attractive in appearance and suitable for mass production at relatively low cost.
Other novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawing, in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for illustration and description only and is not intended as a definition of the limits of the invention.
Certain terminology and derivations thereof may be used in the following description for convenience in reference only, and will not be limiting. For example, words such as xe2x80x9cupward,xe2x80x9d xe2x80x9cdownward,xe2x80x9d xe2x80x9cleft,xe2x80x9d and xe2x80x9crightxe2x80x9d would refer to directions in the drawings to which reference is made unless otherwise stated. Similarly, words such as xe2x80x9cinwardxe2x80x9d and xe2x80x9coutwardxe2x80x9d would refer to directions toward and away from, respectively, the geometric center of a device or area and designated parts thereof. References in the singular tense include the plural, and vice versa, unless otherwise noted.